Install the client-side highlighter

Download dp.SyntaxHighlighter.
Uncompress its content under a new /skins/common/SyntaxHighlighter folder in your MediaWiki installation (don’t forget to make sure the files can be read by the web server; for instance, on Linux you may use chown apache.apache -R *).

In the skin template you are using for your MediaWiki site, insert the necessary code as required. In my example, I use the default /skins/MonoBook.php template into which I added the following:

Just before the closing </head> tag:
Just before the closing

tag:

Note that you must include a reference to each source file corresponding to the type of programming language you want to highlight.
Have a look under the /skins/common/SyntaxHighlighter/Scripts/ folder to see which languages you can highlight; there are a lot more than the few I use on my site.

Install the WikiMedia extension

I’ve created a small extension to WikiMedia to allow us to enclose any source code in a new <codesyntax> tag.
Click on the View Plain option below and copy-paste the following code into a new file that you will save under /extensions/syntaxhighlighter.php (again, make sure this is readable by the webserver).

Usage

To highlight code in your MediaWiki pages, just enclose your source code with the new <codesyntax> tag. This tag takes a lang attribute to specify the options that normally would be listed in the class attribute in the dp.SyntaxHighlighter documentation.